1. Field of the Invention
The present invention pertains to a hydrodynamic coupling device, especially a hydrodynamic torque converter, including a housing arrangement, a turbine wheel, which rotates around an axis of rotation in the housing arrangement, and a bridging clutch arrangement for the optional production of a torque-transmitting connection between the housing arrangement and the turbine wheel. The bridging clutch arrangement includes at least one first friction element, which can rotate together with the housing arrangement and which has at least a first friction surface, and at least one second friction element, which can rotate together with the turbine wheel and which has a second friction surface, which can be brought into frictional contact with a first friction surface of the first friction element. A first surface channel arrangement with first channel sections not open at the radially inner ends and second channel sections not open at the radially outer ends is provided in the friction surface of one of the friction elements. A second surface channel arrangement extending in the circumferential direction is provided in the friction surface of the other friction element, by means of which second channel arrangement the first channel sections and the second channel sections are brought into fluid-conducting connection with each other when frictional contact is established between the first friction element and the second friction element.
2. Description of the Related Art
A hydrodynamic coupling device in the form of a hydrodynamic torque converter is known from U.S. Pat. No. 6,047,806, as shown in FIGS. 1 and 2 herein. This hydrodynamic torque converter 10 comprises a housing arrangement 12 with a housing cover 14 and a pump shell 18, which forms an essential component of a pump wheel 16. On its inner surface, this pump shell 18 carries a plurality of pump vanes 20, arranged in a row in the circumferential direction around an axis of rotation A. In the interior space 22 of the housing arrangement 12, furthermore, a turbine wheel 24 is provided. Radially on the outside, the turbine wheel 24 has a turbine shell 26 with a plurality of turbine vanes 28 supported thereon. Radially on the inside, the turbine wheel 24 can be connected nonrotatably to a power takeoff element 32, such as a transmission input shaft, by way of a turbine hub 30.
A bridging clutch arrangement 34 is provided to establish a direct torque-transmitting connection between the housing arrangement 12 and the turbine wheel 24. In the example shown here, this coupling arrangement comprises a piston 36, serving as a friction element, which is connected nonrotatably to the turbine wheel 24, namely, to the turbine wheel shell 26. On the side facing the housing cover 14, the piston 36 carries a ring-like friction lining 38. This lining can be made of suitable material such as fiber-reinforced polymer material to achieve the desired frictional relationships. In this case, the housing cover 14 serves as the opposing friction element; that is, the part of its surface which is axially across from the friction lining 38 serves as the opposing friction element. By increasing the fluid pressure in a space 40, which is formed essentially between the piston 36 and the pump wheel shell 18, and which also contains the turbine wheel 24, with respect to a space 42, which is formed essentially between the housing cover 14 and the piston 36, the piston 36, the radially inner part of which is able to slide along the turbine wheel hub 30 but is guided in a fluid-tight manner, is pressed toward the housing cover 14 so that the friction lining 38 arrives in frictional contact with the housing cover 14. FIG. 2 shows an axial view of the friction lining 38, namely, a view of the side which is across from the housing cover 14 and which thus provides the friction surface 44. A surface channel arrangement 46 includes a plurality of more-or-less radially oriented first channel sections 48, arranged in sequence around the circumference, which are open at the radially outer ends and closed at the radially inner ends. In addition, a plurality of second channel sections 50 is provided, which are offset from the first channel sections 48. These second channel sections 50 are closed at the radially outer ends and open at the radially inner ends. The first channel sections 48 and the second channel sections 50 are not connected directly to each other. A ring-shaped groove 54, however, is provided as a second surface channel arrangement on the frictionally effective surface 52 of the housing cover 14; this groove is formed as a circular ring passing around the axis of rotation A. The first channel sections 48 and the second channel sections 50 extend far enough from their radially outer and radially inner ends that they at least partially overlap the ring-shaped groove 54. When frictional contact is established between the friction lining 38 and housing cover 14, therefore, fluid from the first space 40 can enter the first channel sections 48 radially from the outside. From these first channel sections 48, the fluid then passes into the ring-shaped groove 54, from which the fluid then can emerge via the second channel sections 50 radially on the inside and thus arrive in the second space 42. It is therefore ensured that, even when the bridging clutch arrangement 34 is active, fluid can be exchanged between the two spaces 40, 42 and thus an exchange of fluid can take place in the entire interior space 22 to prevent the fluid from overheating. This is especially important in the case of converters of the two-line type. The first surface channel arrangement 46 with its channel sections 40 and 50 and the second surface channel arrangement with its ring-shaped channel 54 also ensure that the fluid flowing from the first space 40 to the second space 42 remains for a comparatively long time in the area of the frictionally active surfaces, so that an additional amount of heat can be carried away from this area, which is subject to very severe thermal loads.
So that defined fluid flow relationships between the first space 40 and the second space 42 can be provided in an arrangement of this type, the flow cross sections of the two surface channel arrangements 46, 54 are provided with defined ratios. It has been found, however, that especially the circular ring-like groove 54 suffers from the problem of that its open flow cross section decreases over the course of its service life.
The essential reason for this is that the friction surface 44, which makes contact with the housing cover 14, is on a friction lining 38, which is subject to a certain amount of abrasion. This abrasion, however, will not occur where the friction lining 38, i.e., the area of the friction surface 44 thereof, is opposite the groove 54, because there is no frictional contact here. Therefore, over the course of time, an excess thickness will develop, which projects more and more deeply into the groove 54, thus reducing its flow cross section.
The task of the present invention is to provide a hydrodynamic coupling device of the type described above in which measures are taken to reduce the change in the fluid flow relationships which occur as a result of wear.
According to the invention, essentially for each part of the friction surface of the one friction element which is across from the second surface channel arrangement when in a first relative rotational position of the first friction element with respect to the second friction element, a second relative rotational position is provided, in which this same part of the friction surface is in contact with the friction surface of the other friction element, instead of being across from the channel, where there is no friction.
In the present invention, measures are taken to ensure that there are essentially no friction surface areas present which are not subjected to friction over the course of their service life. Thus it is ensured that, especially when the clutch is slipping, that is, when the two friction elements with the friction surfaces which are interacting frictionally with each other are rotating at different speeds, essentially all parts of the friction surfaces become frictionally active once during each complete relative rotation of these two elements with respect to each other, and thus abrasion occurs uniformly over all of the surfaces.
This change between a state in which a certain friction surface area is across from the second surface channel arrangement and a state in which this same friction surface area is in contact with the other friction surface can be achieved by allowing the radial distance between the second surface channel arrangement and the axis of rotation to change in the circumferential direction. In the case of an embodiment which is especially preferred for manufacturing reasons, it is possible for this purpose to design the second surface channel arrangement in the form of a circle with a center which is eccentric with respect to the axis of rotation. To ensure that the critical friction surface areas on the one friction element can become frictionally active in the case of the channel arrangement which changes once between a maximum and a minimum as it passes around the entire circumference as a result of the introduction of an eccentricity, it is also proposed that the eccentricity of the center of the circle with respect to the axis of rotation be equal to at least approximately half the radial width of the second surface channel arrangement in the friction surface of the other friction element.
The components which are used in hydrodynamic coupling devices and which are frictionally active have a certain play in the radial direction as a result of their connection to, for example, the housing arrangement for rotation in common, this connection often being produced by sets of teeth. This play is superimposed on the change in the radial position of the second surface channel arrangement, so that, even if the eccentricity in the case of, for example, a second surface channel arrangement with an eccentric design is somewhat smaller than half the radial width of this second arrangement, the statistical movement in the radial direction which occurs as a result of tolerances which allow movement will be superimposed on this eccentricity. Even in this case, therefore, by inclusion of this statistical movement in the radial direction, it will be ensured that all parts of the opposite surface will come into contact once per revolution with the friction surface in which the second surface channel arrangement is provided. It should also be pointed out that, according to the principles of the present invention, literally all parts of the surface do not have to come into contact with the friction surface of the other friction element in which the second surface channel arrangement is provided. Depending on the width or flow cross section of the second surface channel arrangement, it is possible for a thin web, for example, to remain intact, part of which can break off by itself perhaps or which is so thin that the flow cross section of the second surface channel arrangement will not be significantly reduced.
In an especially preferred embodiment especially for avoiding imbalances, it can be provided that the second surface channel arrangement is designed in the form of an ellipse. In addition, the change between a frictionally active and a frictionally inactive state of certain parts of the surface can be achieved by designing the second surface channel arrangement with waves extending around in the circumferential direction. It should be noted here that an undulating or wave-like shape can obviously be superimposed on a circular form or an elliptical form or any other form which is rotationally symmetric or is not rotationally symmetric to the axis of rotation.
The other of the friction elements can have a metal friction surface, and the one of the friction elements can-have a friction surface formed on a friction lining to provide defined frictional relationships.
So that high torques can be transmitted between the housing arrangement and the turbine wheel, it is also possible for the other of the friction elements to have a friction surface on both axial sides, each of these being provided with a second surface channel arrangement. In this type of embodiment, therefore, there are several different surface pairings which can be brought into interaction with each other, so that the corresponding overall frictional surface area is increased. So that it is possible to avoid the occurrence of imbalances in an arrangement of this type, that is, in an arrangement in which the second friction element is frictionally active on both sides and has a surface channel arrangement on both sides, it is proposed that the surface channel arrangements provided on both axial sides be essentially the same, but angularly offset with respect to each other in the circumferential direction.
According to another embodiment, it is possible for the second surface channel arrangement to be interrupted in at least one circumferential area. Regardless of whether this circumferential interruption has a uniform or a changing radial distance from the axis of rotation, providing the second surface channel arrangement with at least one circumferential interruption represents another method of ensuring that the parts of the opposing friction surface which would otherwise always be opposite the surface channel arrangement are contacted and thus subjected to abrasion, namely, by this interruption of the second channel arrangement.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.